It is known for satellite set-top box arrangements to provide multi-channel reception capability, for example for PVR (personal video recorder) type applications. For such applications, each channel must be receivable independently of each other channel selected for reception. This is particularly important in satellite applications because the signal received from an outdoor unit covers a wider frequency range than the operating range of a typical set-top box and contains two polarisations which effectively overlap. To accommodate this, it is known to have one or two cable feeds from the outdoor unit to the set-top box, each of which can potentially carry any channel from the spectrum of a received signal.
FIG. 1 of the accompanying drawings illustrates a typical multi-channel tuner arrangement for such an application. The cable feeds are shown at 1 and 2 and are connected to independent signal paths 3 and 4, respectively, although a single cable feed connected to both signal paths may also be used. The signal paths are substantially identical so that only the path 3 is shown and will be described in detail.
The signal path 3 comprises a zero intermediate frequency (ZIF) tuner 5 connected to a demodulator arrangement 6. The tuner 5 comprises a quadrature mixer 7, which receives a broadband input signal from the cable feed 1 directly or via other stages (not shown), such as a low noise amplifier and an automatic gain control arrangement. The mixer 7 receives quadrature signals from a local oscillator (LO) 8 controlled by a phase locked loop (PLL) synthesiser 9. The PLL 9 receives a reference frequency signal from a reference oscillator 10, which is common to both of the tuners, although independent reference oscillators could alternatively be provided.
Tuner operation is controlled by a common controller 11, which could also be replaced by separate controllers for the individual tuners. The synthesiser 9 is controlled in accordance with a request from a user for reception of a selected channel. The synthesiser 9 controls the oscillator 8 to provide quadrature signals whose frequency is substantially equal to the centre frequency of the channel selected for reception. The mixer 7 converts the selected channel to in-phase I and quadrature Q baseband signals centred around 0 Hz.
The signals I and Q are supplied to respective low pass filters (LPF) 12 and 13, which filter the baseband signals so as to attenuate or remove signal energy from non-selected channels. The filters 12 and 13 may be connected directly to the mixer 7 or via other stages (not shown), such as amplifiers and automatic gain control arrangements. Similarly, the output signals of the filters 12 and 13 may be supplied directly to the tuner outputs or may be supplied via other stages (not shown), such as amplifiers and automatic gain control arrangements.
The filtered I and Q signals from the tuner 5 are supplied to respective analogue/digital converters (ADC) 14 and 15, which sample the quadrature components and convert them to respective independent data streams. The data streams are supplied to a demodulator block 16, which typically filters, fine tunes, and demodulates the received quadrature signal. The demodulated signals are then supplied to a forward error correction (FEC) block 17, which performs the appropriate error correction in accordance with the modulation standard of the received channel. The block 17 supplies the output signal at an output 18 of the tuner arrangement.
The broadband signals supplied via the cable feed 2 are likewise processed by the second ZIF tuner 19 and the second demodulator arrangement 20 and the resulting signals appear at a second tuner arrangement output 21 as a separate transport stream. Each of the transport streams may be parallel or analogue or the streams may be multiplexed together. Although only two signal paths 3 and 4 are shown, any number of such paths may be provided according to application requirements.
Although such an arrangement functions satisfactorily, it is relatively complex and expensive. In particular, most or all of the individual functions have to be duplicated or multiplicated.